This is generally in the field of improved compositions for tissue engineering, specifically scaffolds incorporating defined densities of matrix-enhancing molecules for improving matrix protein production of cells, without inducing excessive proliferation of the cells.
In fields where cell growth, maintenance, or production of exogenous factors are important, such as in the field of tissue engineering, cells are often grown on solid substrates or scaffolds which provide a suitable substrate for cell adhesion and growth. These scaffolds may be made of natural or synthetic materials.
Biomaterials developed for tissue engineering and wound healing applications need to support adequate cell adhesion while being replaced by new tissue synthesized by those cells. In order to maintain proper mechanical integrity of the tissue, the cells must generate sufficient extracellular matrix (ECM). Decreased ECM production by cells in tissue engineering scaffolds may lead to reduced structural integrity of the developing tissue.
In order to optimally promote adhesion to such materials, researchers have investigated attachment of cell adhesion ligands, such as the RGD peptide, to surfaces of biomaterials (Massia & Hubbell, Anal. Biochem. 187:292-301 (1990); Hem & Hubbell, J. Biomed. Mater. Res. 39:266-276 (1998); Dee, et al. J. Biomed. Mater. Res. 40:371-377 (1998); Tong & Shoichet, J. Biomed. Mater. Res. 42:85-95 (1998); Zhang, et al., Biomaterials 20:1213-1220 (1999)). However, an increase in cell adhesion can adversely affect ECM production (Mann, et al., Biomaterials 1999). In addition, there exists a substantial need to increase ECM production, even in unmodified scaffolds, as the proteins in the ECM largely determine the mechanical properties of the resultant tissue and are often needed to replace the functions of a biodegradable scaffold material. The mechanical properties of the resultant tissue are particularly important in applications such as tissue engineered vascular grafts and orthopedic tissue engineering wherein failure can occur due to poor mechanical integrity.
Researchers have also attached growth factors such as TGF to a tissue engineering matrix via a polymeric tether such as a polyethylene glycol. See PCT/US96/02851 “Cell Growth Substrates with Tethered Cell Growth Effector Molecules” Massachusetts Institute of Technology. There are a number of references that TGF-beta can be bound to or dispersed within a synthetic or natural polymeric carrier for controlled release of active growth factor. See, for example, “Collagen and heparin matrices for growth factor delivery”, Schroeder-Tefft, et al. Journal of Controlled Release 49(2-3), 291-298 (1997); “In vitro characterization of transforming growth factor-beta-1-loaded composites of biodegradable polymer and mesenchymal cells. Nicoll, et al. Cells and Materials 5(3), 231-244 (1995). EP 00428541“Collagen Wound healing Matrices and Process for their Production” to Collagen Corporation; U.S. Pat. No. 6,013,853 “Continuous release polymeric implant carrier” to Athanasiou, et al. Additional reference relate to the use of TGF-beta in tissue engineering scaffolds to enhance cell or tissue growth or proliferation, particularly of bone. See EP 616814 “Ceramic and Polymer-Based Compositions for Controlled Release of Biologically Active TGF-Beta to Bone Tissue, and Implants Using The Compositions” by Bristol-Myers Squibb Company.
However, none of these disclosures disclose how one can achieve enhanced production of extracellular matrix, while not increasing cellular proliferation.
It is therefore an object of the present invention to provide tissue engineering scaffolds which promote formation of ECM, to enhance the formation of tissue with good mechanical properties, on and within the tissue engineering scaffold, i.e., with little or no increase in cellular proliferation.